Here's what Mark Udall (D-Colo.), a prominent defender of civil liberties, had to say about Mueller's admission:

"I am concerned the FBI is deploying drone technology while only being in the 'initial stages' of developing guidelines to protect Americans' privacy rights," Udall said in a statement. "I look forward to learning more about this program and will do everything in my power to hold the FBI accountable and ensure its actions respect the U.S. Constitution."

“Everybody wants their privacy, but I don’t know how you’re going to maintain it,” Bloomberg said on his weekly radio show. “It’s just we’re going into a different world, uncharted, and, like it or not, what people can do, what governments can do, is different ... you can’t keep the tides from coming in.”